The advent of new biomedical imaging technique has enabled significant progresses in how we image humans and animals. In particular, the emergence in the mainstream of new modalities, such as diffuse optical tomography (DOT) has enabled researchers to image hemodynamic in vivo in a non invasive fashion. The relative low absorption and low scattering in the 600-1000 nm spectral range allow detection of photons travelling through several centimeters of biological tissue. Coupled with accurate models of light propagation, the NIR techniques enable imaging of deep tissue with boundary measurements using non-ionizing, low dose radiation. Applications of clinical significance have emerged for this modality, among those; breast cancer detection and neuronal activation measurement for cognitive studies are applications currently being actively pursued. By using different wavelengths, it is possible to map changes in hemodynamic and oxygenation levels to changes in light intensity. Diffuse optical tomography can also be performed with the combination of contrast agents absorbing light or having fluorescent properties. The imaging problem then aims to also recover the contrast agent localization and concentration.
Optical biomedical DOT imaging includes illuminating the tissue or turbid medium object with a light source and measuring the light leaving the tissue with a detector. Typically, such as described in U.S. Pat. No. 6,958,815 and US patent applications 2006/0184043 and 2009/0118622, a model of light propagation in the medium is developed and parameterized in terms of the unknown optical properties, scattering and/or absorption and/or concentration of the contrast agent, as a function of position in the tissue. The imaging problem consists in recovering the optical parameters, namely absorption, scattering, agent concentration, by using distinct illumination and detection positions.
The reconstructed image is a three-dimensional map of optical properties including endogenous absorption, scattering or fluorescence and exogenous compounds (absorption or fluorescence). With these reconstructed images, physiological measures can be performed such as blood oxygen saturation, blood volume, contrast agent concentration and dynamical uptake. These images enable to establish important physiological measurements such as metabolic activity, angiogenesis, hypoxia and pH, hyper-metabolism, micro-calcifications, protein expression.
Until now, optical mammography has mostly been implemented by positioning a series of local light sources and detection points at different positions on the breast surface depending on the configuration. In some implementation, a circular configuration of sources and detectors are used in combination with a multiplexing scheme. In others, sources and detectors are positioned in reflection or in opposite sides of parallel plates compressing the breast. In the latter configuration, the sources can be scanned mechanically or optically (with galvanometer mirrors) providing high-density measurements. The detection in this configuration can be done with either discrete detectors or a sensitive camera. These imaging techniques have a drawback however: to get dense measurements one has to scan or multiplex every light position, thereby limiting the frame rate.